Self-healing, pH-sensitive and shape memory hydrogels based on acylhydrazone and hydrogen bonds

Smart hydrogels have wide potential in biological field owing to their self-healing property, pH or temperature sensitivity. However, the preparation of smart hydrogels often requires complicated synthesis process, and the single functionality of hydrogels might limit their application. To solve these problems, we developed a self-healing, pH-sensitive and shape memory hydrogel of poly (diacetone acrylamide- co -acrylamide -co -acrylic acid)/alginate (PDAAc-A), taking advantage of the Schiff-base reaction and the hydrogen bonding interaction in a one-step method. The tensile modulus, fracture stress, fracture strain and toughness of the developed PDAAc-A3 hydrogel are 0.021 MPa, 0.013 MPa, 7.5 mm/mm and 0.07 MJ/m 2 , respectively. The dynamic and reversible acylhydrazone and hydrogen bonds endow hydrogels with self-healing property and pH-sensitive gel-sol transformation ability. The tensile tests demonstrate that the self-healing efficiency of hydrogel could reach up to 85% after about 30 min. Furthermore, PDAAc-A hydrogel exhibits pH-sensitivity during drug release. In PBS solution with pH value of 5, the hydrogel shows the fastest drug release rate and the highest drug release ratio, which is near 100% after about 4 h. Moreover, in 1 M ferric chloride solution, the shape memory time, shape memory ratio and shape recovery ratio of the resultant hydrogel are 2 min, 100% and 100%, respectively.